[Intel-gfx] [PATCH 1/2] drm/i915: time out of load detect busy-waits

[Daniel Vetter]

If we try to do that and the scanlines just wouldn't advance, we
busy-hang the machine holding the modeset mutex. Not great for
debugging.

References: https://bugzilla.kernel.org/show_bug.cgi?id=43020
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/intel_crt.c |   21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 0976137..d30779e 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -383,6 +383,7 @@ intel_crt_load_detect(struct intel_crt *crt)
 	} else {
 		bool restore_vblank = false;
 		int count, detect;
+		unsigned long timeout;
 
 		/*
 		* If there isn't any border, add some.
@@ -407,22 +408,32 @@ intel_crt_load_detect(struct intel_crt *crt)
 		/*
 		 * Wait for the border to be displayed
 		 */
-		while (I915_READ(pipe_dsl_reg) >= vactive)
-			;
-		while ((dsl = I915_READ(pipe_dsl_reg)) <= vsample)
-			;
+		if (wait_for(I915_READ(pipe_dsl_reg) >= vactive, 1000))
+			DRM_ERROR("timed out waiting for vactive in "
+				  "load_detect, scanline: %u\n",
+				  I915_READ(pipe_dsl_reg));
+		if (wait_for((dsl = I915_READ(pipe_dsl_reg)) <= vsample, 1000))
+			DRM_ERROR("timed out waiting for vsample in "
+				  "load_detect, scanline: %u\n",
+				  I915_READ(pipe_dsl_reg));
 		/*
 		 * Watch ST00 for an entire scanline
 		 */
 		detect = 0;
 		count = 0;
+		timeout = jiffies + msecs_to_jiffies(1000);
 		do {
 			count++;
 			/* Read the ST00 VGA status register */
 			st00 = I915_READ8(VGA_MSR_WRITE);
 			if (st00 & (1 << 4))
 				detect++;
-		} while ((I915_READ(pipe_dsl_reg) == dsl));
+		} while ((I915_READ(pipe_dsl_reg) == dsl) &&
+			 !time_after(jiffies, timeout));
+
+		if (time_after(jiffies, timeout))
+			DRM_ERROR("timed out while load-detecting, scanline: %u\n",
+				  I915_READ(pipe_dsl_reg));
 
 		/* restore vblank if necessary */
 		if (restore_vblank)
-- 
1.7.10